Sahih Muslim Book 3, Hadith Number 729.

Chapter : What should be uttered while entering the privy ?.

Anas reported: When the Messenger of Allah (may peace be upon him) entered the privy, and in the Hadith transmitted by Hushaim (the words are): When the Messenger of Allah (may peace be upon him) entered the lavatory, be used to say: O Allah, I seek refuge in Thee from wicked and noxious things.